The use of manganese and cerium co-activated gadolinium magnesium zinc pentaborate phosphors in mercury-vapor discharge lamps for fluorescent lighting applications is well established. The phosphor, which may be represented by the general formula (Ce,Gd)(Mg,Zn,Mn)B5O10, is a broad-band red-emitting phosphor which has a deeper red color than the most common red-emitting phosphor, europium-activated yttrium oxide, Y2O3:Eu, and is useful for improving the Color Rendering Index (CRI) of mercury-vapor fluorescent lamps.
For example, the use of Gd(Zn,Mg)B5O10:Ce,Mn to provide high color rendering in high-output compact fluorescent lamps is disclosed in U.S. Pat. No. 7,138,757, while the same phosphor written as (Ce,Gd)(Zn,Mg)B5O10:Mn is disclosed for use in low-pressure gas discharge lamps for the same purpose in U.S. Pat. No. 6,794,810. In U.S. Pat. No. 7,259,509, the phosphor is disclosed for use in mercury low-pressure discharge lamps for illuminating plants and the related phosphor Gd1−x−yCexTby(Mg)1−pMnpB5O10 is disclosed for use in fluorescent lamps with CRI values of at least 82 in U.S. Pat. No. 5,612,590.
The synthesis of metaborate phosphors with the general composition (Y,La)1−x−y−zCexGdyTbz(Mg,Zn)1−pMnpB5O10 (which includes CexGdy(Mg,Zn)1−pMnpB5O10) is described in U.S. Pat. No. 4,319,161. The method of producing these pentaborate phosphors involves dry mixing oxides of the rare earth elements, the oxide or hydrated carbonate-hydroxide of magnesium, manganese carbonate, the oxide of zinc and boric acid, and then subjecting the mixture to two or three firings in a weakly reducing atmosphere, typically with a comminution step in between.
Such repeated grinding and firing methods are labor intensive, more time consuming, and ultimately more costly than if the phosphor could be prepared in fewer steps, in particular a single-step firing method. Thus, it would be advantageous to have a simpler, more cost-effective method to produce a (Ce,Gd)(Mg,Zn,Mn)B5O10 phosphor.